The present invention relates to the field of mechanical focusing and convergence devices for optical systems, and more particularly to an improved mechanical convergence fixture for projection-type liquid crystal projectors. The predominant current usage of the inventive mechanical convergence fixture is in commercial video projection devices wherein accuracy of adjustment, economy of manufacture and ruggedness are all important factors.
In a liquid crystal projector, white source light is separated into beams of its three primary colors. Each beam is then infused with an image by a liquid crystal light valve or micro-LCD. Finally, the three beams are recombined into a single image and projected onto a display device (a screen).
The micro LCD""s generate a representation of the image to be projected by using many small picture elements or pixels. Therefore, the above mentioned beams of light that emerge from the micro-LCD""s are pixellated representations of the particular color components of the image. Thus, an accurate projected image requires that the pixels of the three infused beams be precisely aligned during the recombination step, meaning that the micro-LCD""s themselves must be carefully positioned. In order to optimally orient the micro-LCD""s the following requirements must be met.
(1) 6 degree of freedom (dof) adjustment capability must be available. Both rotation and linear translation with respect to three perpendicular axes are required in order to ensure that proper image alignment can be caused to occur.
(2) Adjustment mechanisms must have high resolution controls. Because of the small size of the pixels, direct manual adjustments are too crude to achieve proper alignment. Some sort of interface must be provided which can transform relatively large-scale operator inputs into micro-LCD motions of a magnitude commensurate with the pixel size.
(3) Adjustment mechanisms must provide positive positioning constraints. Since multiple operations are required to tune all 6 degrees of freedom, intermediate adjustments must have some amount of resistance to motion. Positioning devices typically have some sort of final locking mechanism, but to activate and deactivate that mechanism numerous times over the course of adjustment is cumbersome and often impossible. Therefore, any robust positioning device must provide for physical locating effects, rather than relying on balance, gravity or friction.
(4) The individual magnification of each image must be independently adjustable. There must be a means for making slight adjustments to the projected size of the image from any projection device. This means must be simple, inexpensive, and easy to use such that adjustments can be made quickly during the production process.
Conventional positioning systems have either provided limited adjustment capability or else have use complicated mechanisms. For example, in U.S. Pat. No. 5,418,586 issued to Fujimori, a light valve positioning system is disclosed which uses a combination of plates, posts, and screws to provide the full 6 degree of freedom adjustment capability. However, while the mechanism taught by Fujimori provides a significant improvement in the field, it utilizes 6 major components and 14 adjustment screws. In addition, in spite of Fujimori""s own listing of problems associated with eccentric pins (manufacturing difficulty, increased part count due to supporting components, non-linear relationship between rotational input and linear translation output, and the like), the mechanism of Fujimori still includes three such pins. Also, the mechanism of Fujimori utilizes a number of direct manual adjustments, making precise control difficult. For instance, a typical adjustment procedure used according to the Fujimori teachings is represented in the rotating of the liquid crystal valve about a vertical axis. This procedure involves rotation a flat head screwdriver in a slot formed by a notch in a light fixing plate and a hole in a lower adjustment plate. In this operation, the scales of the operator inputs are completely out of scale compared to the required adjustments, making proper alignment impossible. In addition, because the adjustment actuator (the flat head screwdriver) is removed once the desired rotation is achieved, the position of the light fixing plate is not positively secured. This allows motion to occur during the actual fixing process when the fixing screws are tightened, potentially causing misalignment of the liquid crystal light valve.
Many of these concerns have been addressed in a copending patent application Ser. No. 08/970,957 entitled MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD, which has an inventor in common with this present invention. The MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD provides all of the requirements discussed above and avoids the pitfalls. Indeed, for some applications the MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD may be superior to the present invention. However, the MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD is still quite complicated and is relatively expensive to manufacture.
It would be advantageous to have a device for positioning a micro LCD in a projection device so as to provide for optimal accuracy of adjustment and ruggedness, while maintaining optimal simplicity and economy. However, to the inventor""s knowledge, no prior art method or means has achieved this combination of goals. Such devices have all been either to complicated and expensive and/or too difficult to adjust, or else have been overly delicate and/or expensive to produce.
Accordingly, it is an object of the present invention to provide an optical-mechanical convergence device which will provide for accurate and easy positioning of a liquid crystal display (xe2x80x9cLCDxe2x80x9d) in a projection apparatus.
It is still another object of the present invention to provide a method and apparatus for positioning a micro-LCD which is economical to manufacture.
It is yet another object of the present invention to provide a method and apparatus for positioning a micro-LCD which is rugged in that the position of the micro-LCD will not shift when subjected to normal shock and vibration.
It is still another object of the present invention to provide an apparatus and method for adjusting the magnification of each device channel in an LCD projector in order to make all projected images the same size.
Briefly, the preferred embodiment of the present invention is a frame for securing a micro-LCD to an associated field lens. The frame is positioned in relation to a chassis using an external three axis linear stage (alignment assembly) and, when in position, is affixed with an adhesive to a plurality of locating studs which are rigidly affixed to the chassis. The expensive alignment assembly is the removed. The alignment assembly is then an assembly device rather than a component of the shipped product, thereby greatly reducing the cost of the shipped product.
An advantage of the present invention is that, since size and expense of the adjustment mechanism are not critical (since the adjustment mechanism stays behind to be reused), then the adjustment mechanism can be made to be very accurate and easy to use.
A further advantage of the present invention is that the micro-LCD can be very accurately positioned and held in place.
Yet another advantage of the present invention is that the micro-LCD is rigidly affixed on a very light frame which is not readily susceptible to shock and vibration.
Still another advantage of the present invention is that the per unit expense is greatly reduced.
Yet another advantage of the present invention is that an optical element (a field lens) can be re-positioned axially to provide slight adjustments of the magnification of the individual image devices, thereby allowing very high resolution alignment.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the described mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawing.